The present invention relates to powder coating systems. More particularly, the invention relates to methods and apparatus for cleaning powder coating systems to facilitate color change operations.
Known powder coating systems typically include a powder source, a powder pump, a powder spray gun, a hose connecting the pump to the gun and a pick-up tube that feeds powder from the powder source to the pump. Powder coating systems usually are designed to work with a plurality of colors of powder coating material. For many such systems, especially larger systems that use a plurality of guns to apply powder to larger objects, the powder coating material of the previous color must be removed from the system before the next color of powder coating material can be used. In larger systems this can involve a significant amount of down time to clean all the powder out of the system including having to purge powder residue from the pick-up tube, the pump, the hose and the gun. The faster the purging can be accomplished, the less is the overall down time required for a color changeover.
Various purging systems have been developed including those shown in U.S. Pat. Nos. 4,248,379 and 5,341,989, owned in common by the assignee of the present invention, the entire disclosures of which are fully incorporated herein by reference. However, to date no single system effectively purges and cleans the pick-up tube, pump, hose and gun in a single operation without substantial disassembly of the system and with minimum operator involvement.
It is desired, therefore, to provide new methods and apparatus for purging powder coating system components with reduced time and effort in order to speed up a color change operation.
In accordance with one embodiment of the invention, a purging apparatus is provided for a powder coating system of the type having a powder supply, a powder pump that receives powder from the powder supply through a suction pick-up tube, a powder applicator such as a spray gun and a powder hose that connects the pump to the gun. The purging apparatus may include a purge air switch assembly. A first air source provides air at purge pressure to a first inlet of the purge air switch assembly. A second air source provides flow rate air to a first pump inlet and atomizing air for the pump to a second inlet of the purge air switch assembly. During powder spraying operations the atomizing air passes through the purge air switch assembly to a second pump inlet. Powder is drawn up the tube and into the pump through a powder inlet by suction produced by the flow rate air into the pump. A purge inlet is associated with the powder inlet to the pump. During color change operations, the purge air switch assembly, operating in response to a purge control signal from a controller, shifts the position of the purge switch to cutoff the normal atomizing air flow to the pump and connects purge air to the atomizing inlet at the pump and to a purge inlet near the powder inlet of the pump, whereby the pump, hose and gun can be purged at the same time. The present invention also contemplates the optional use of purge air into the flow rate air port of the pump.
In accordance with another aspect of the invention, apparatus is provided for cleaning a powder pick-up tube in a powder coating system. The apparatus includes a powder pick-up tube; means for mounting the tube on a vessel; a wiper device closely received on the tube exterior and stationary with respect to the tube; the wiper device removing powder from the tube exterior as the tube is at least partially withdrawn from the vessel.
The present invention also contemplates the methods embodied in the use and/or operation of the above described apparatus.
These and other aspects and advantages of the present invention will be apparent to those skilled in the art from the following description of the preferred embodiments in view of the accompanying drawings.